Coating compositions for electrode compositions and their methods of making

ABSTRACT

Compositions and methods of making are provided for coated electrodes and batteries comprising the same. The compositions may comprise a base composition having an active material selected from the group consisting of LiCoO 2 , LiMn 2 O 4 , Li 2 MnO 3 , LiNiO 2 , LiMn 1.5 Ni 0.5 O 4 , LiFePO 4 , Li 2 FePO 4 F, Li 3 CoNiMnO 6 , Li(Li a Ni x Mn y Co z )O 2 , and mixtures thereof. The compositions may also comprise a coating composition that covers at least a portion of the base composition, wherein the coating composition comprises a non-metal or metalloid element. The methods of making comprise providing the base composition and a doped carbon coating composition, and mixing the coating composition with the base electrode composition at an elevated temperature in a flowing inert gas atmosphere. The coating composition may be a nitrogen-doped carbon composition a nitrogen doping element selected from the group consisting of: pyridine, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, and mixtures thereof.

STATEMENT OF GOVERNMENT INTEREST

The invention was made with government support under contract numberDE-AC05-00OR22725 by the Department of Energy. The Government hascertain rights in the invention.

BACKGROUND

Electrical energy storage systems have attracted significant attentionwithin the past few decades due to the sustained interest in alternativeenergy sources which stems from the gradual depletion of oil resourcesaround the world. From this point of view, the development of clean andhighly efficient energy storage systems is becoming an even more urgentneed. Advanced energy storage systems such as lithium-ion batteries areimportant approaches to mitigate energy shortage and global climatewarming issues that the world is currently facing. High power and highenergy density are essential to batteries for applications in electricvehicles, stationary energy storage systems for solar and wind energy,as well as smart grids.

Because conventional lithium-ion batteries are inadequate to meet theseneeds, advanced materials with high capacity and fast charge-dischargecapability are desirable for next generation lithium-ion batteries.Additionally, it is desirable to develop an electrode material withimproved conductivity to further improve the rate capability and/orcycling performance.

SUMMARY

Compositions and methods of making are disclosed for modified electrodecompositions for use in batteries.

In one embodiment, the electrode for the battery comprises a basecomposition having an active material capable of intercalating the metalions during a discharge cycle and deintercalating the metal ions duringa charge cycle, wherein the active material is selected from the groupconsisting of LiCoO₂, LiMn₂O₄, Li₂MnO₃, LiNiO₂, LiMn_(1.5)Ni_(0.5)O₄,LiFePO₄, Li₂FePO₄F, Li₃CoNiMnO₆, Li(LiaNi_(x)Mn_(y)Co_(z))O₂,Li_(a)Mn_(1.5-b)Ni_(0.5-c)M_(d)O_(4-x), and mixtures thereof. Theelectrode further comprises a coating composition that covers at least aportion of the base composition, wherein the coating compositioncomprises a non-metal or metalloid element.

In some embodiments, the coating composition comprises a nitrogen-dopedcarbon composition. The nitrogen-doped carbon composition may comprise anitrogen doping element selected from the group consisting of: pyridine,1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,1-ethyl-3-methylimidazolium dicyanamide, and mixtures thereof.

In some embodiments, the active material in the base compositioncomprises LiFePO₄. In other embodiments, the electrode comprises between0.1-20 wt. % carbon and between 0.01-5 wt. % of the non-metal ormetalloid element. In some embodiments, the capacity is at least 10%greater at 3 C, or at least 30% greater at 5 C, when compared with anelectrode having the same base composition without a coatingcomposition.

In certain embodiments, the electrode has a capacity of at least 125mAh/g at a rate of C/10, at least 120 mAh/g at a rate of 1 C, at least110 mAh/g at a rate of 3 C, or at least 98 mAh/g at a rate of 5 C.

In another embodiment, a battery comprises an anode having a basecomposition and a cathode having a base composition with an activematerial capable of intercalating the metal ions during a dischargecycle and deintercalating the metal ions during a charge cycle, whereinthe active material is selected from the group consisting of LiCoO₂,LiMn₂O₄, Li₂MnO₃, LiNiO₂, LiMn_(1.5)Ni_(0.5)O₄, LiFePO₄, Li₂FePO₄F,Li₃CoNiMnO₆, Li(Li_(a)Ni_(x)Mn_(y)Co_(z))O₂, and mixtures thereof. Thebattery further comprises a coating composition that covers at least aportion of the base composition of the cathode or the base compositionof the anode, wherein the coating composition comprises a non-metal ormetalloid element. The battery further comprises an electrolyte capableof supporting reversible deposition and stripping of metal at the anode,and reversible intercalation and deintercalation of the metal at thecathode.

In some embodiments, the active material in the base composition of thecathode comprises LiFePO₄. In other embodiments, the coating compositioncomprises a nitrogen-doped carbon composition. The nitrogen-doped carboncomposition may comprise a nitrogen doping element selected from thegroup consisting of: pyridine, 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazoliumdicyanamide, and mixtures thereof.

In some embodiments, the coating composition comprises1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. Incertain embodiments, the coating composition covers at least a portionof the cathode, forming a coated cathode, wherein the coated cathodecomprises between 0.1-20 wt. % or between 0.01-10 wt. carbon. In otherembodiments, the coating composition forms a coated cathode, and thecapacity is at least 10% greater at 3 C, or at least 30% greater at 5 C,when compared with a cathode having the same base composition and anundoped carbon coating composition. In yet other embodiments, thecoating composition covers at least a portion of the cathode, forming acoated cathode having a capacity of at least 125 mAh/g at a rate ofC/10, at least 120 mAh/g at a rate of 1 C, at least 110 mAh/g at a rateof 3 C, or at least 98 mAh/g at a rate of 5 C.

In certain embodiments, the base composition of the anode comprises atleast 90 wt. % lithium as the primary electrochemically active materialof the anode. In some embodiments, the base composition of the anodecomprises mesoporous metal oxide microspheres, having (a) microsphereswith an average diameter between 200 nm and 10 μm, and (b) mesopores onthe surface and interior of the microspheres, wherein the mesopores havean average diameter between 1 nm and 50 nm and the microspheres have asurface area between 50 m²/g and 500 m²/g.

In some embodiments, the battery is selected from the group consistingof the following battery types: lithium-ion, aluminum-ion,magnesium-ion, sodium-ion, metal-air, and metal-sulfur, wherein themetal is lithium, aluminum, magnesium, zinc, or sodium. In oneparticular embodiment, the battery is a lithium-ion battery. The batterymay have an ability to charge from 0% to 50% of the full range capacityin 6 minutes, or an ability to charge from 0% to 33% of the full rangecapacity in 1 minute. The battery may have a functional dischargecapacity of at least 90% of the initial discharge capacity after 100cycles. The battery may be used in a grid storage application, vehiclebattery application, military application, portable electronic deviceapplication, medical device application, or standard cell size batteryapplication.

In another embodiment, a method of forming a coated electrodecomposition comprises providing a base electrode composition having anactive material is selected from the group consisting of LiCoO₂,LiMn₂O₄, Li₂MnO₃, LiNiO₂, LiMn_(1.5)Ni_(0.5)O₄, LiFePO₄, Li₂FePO₄F,Li₃CoNiMnO₆, Li(Li_(a)Ni_(x)Mn_(y)Co_(z))O₂, and mixtures thereof. Themethod further comprises providing a doped carbon coating composition.The method further comprises mixing the coating composition with thebase electrode composition at an elevated temperature in a flowing inertgas atmosphere.

In some embodiments, the base electrode composition comprises LiFePO₄.In other embodiments, the doped carbon composition is a nitrogen-dopedcarbon composition having a nitrogen doping element selected from thegroup consisting of: pyridine, 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazoliumdicyanamide, and mixtures thereof. In yet other embodiments, the coatingcomposition comprises 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide. In some embodiments, the elevatedtemperature is at least 700° C. and the inert gas is argon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) depicts XRD patterns of LiFePO₄ samples coated withnitrogen-doped carbon layers.

FIG. 1(b) depicts the carbon-content of LiFePO₄ samples usingthermo-gravimetric analysis (TGA).

FIG. 1(c) depicts the Raman spectroscopic analysis for a LiFePO₄ sample.

FIG. 1(d) depicts the thermo X-ray photoelectron spectrometer XPS surveyspectra of a coated LiFePO₄ sample.

FIG. 2(a) depicts the cycling performance of coated LiFePO₄ samples atC/10.

FIG. 2(b) depicts the cycling performance of coated LiFePO₄ samples atC/10, 1 C, 3 C, and 5 C.

FIG. 3 depicts the discharge capacity of untreated and treated(annealed) LiMn_(1.5)Ni_(0.5)O₄ cathodes at C/10, 1 C, 3 C, 5 C, and 10C.

DETAILED DESCRIPTION

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. For example,reference to “a substituent” encompasses a single substituent as well astwo or more substituents, and the like.

As used herein, the terms “for example,” “for instance,” “such as,” or“including” are meant to introduce examples that further clarify moregeneral subject matter. Unless otherwise specified, these examples areprovided only as an aid for understanding the applications illustratedin the present disclosure, and are not meant to be limiting in anyfashion.

As used herein, the following terms have the following meanings unlessexpressly stated to the contrary. It is understood that any term in thesingular may include its plural counterpart and vice versa.

As used herein, the term “lithium-ion” may refer to any ion comprisinglithium, including but not limited to Li⁺.

As used herein, the term “cycle” may refer to the discharge and chargeof the capacity of the battery.

As used herein, the term “functional discharge capacity” may refer to acomparison between the current capacity of the battery and the battery'sinitial capacity. In certain embodiments, the battery is still operablewhen the functional discharge capacity is more than 50%, 60%, 70%, 80%,or 90% of the initial discharge capacity.

As used herein, the terms “secondary” and “secondary battery” may referto rechargeable batteries wherein the electrochemical reactions areelectrically reversible (i.e., the reaction can be reversed by running acurrent into the cell to restore the capacity of the battery). Incertain embodiments, the secondary battery can achieve a number ofcycles (e.g., 100, 1000, 5000, or 10000 cycles) while maintaining afunctional discharge capacity (e.g., the discharge capacity is more than50%, 60%, 70%, 80%, or 90% of the initial discharge capacity).

As used herein, the terms “mesoporous” and “mesoporous structure” mayrefer to a material or composition containing pores. In certainembodiments, the average pore size of the microsphere structure isbetween 1 nanometer (nm) and 50 nm. In other embodiments, the averagepore diameter in the microsphere structure is between 5 nm and 20 nm. Inyet other embodiments, the average pore diameter is between 10 nm and 15nm. In one particular embodiment, the average pore diameter in themicrosphere structure is approximately 12 nm.

As used herein, the terms “C/10,” “C/2,” “1 C,” “2 C,” “5 C,” “10 C,”“20 C,” “30 C,” “60 C,” and the like refer to the “C-rate” orcharge-discharge rate (Amp-hour) of the battery.

As used herein, the terms “treating” or “treated” may refer to theprocess or resulting electrode composition that has been processed orreacted in some manner to improve the conductivity of the composition,thereby improving the rate capability and/or cycling performance of thecomposition. In some embodiments, the composition is treated through anannealing step, doping step, coating step, or combination thereof.

It has been discovered that performance properties of the electrodecompositions may be improved by coating or chemically treating theelectrode (modifying the surface of the electrode, in particular).Certain modifications may improve the rate-capabilities and/or improvedcycling performance of a battery.

In certain embodiments, batteries with improved electrode compositionsmay be used in grid storage applications, vehicle battery applications,military applications, portable electronic device applications, medicaldevice applications, or standard cell size battery applications. In oneparticular embodiment, the battery with an improved electrodecomposition is used for a grid storage application. In anotherparticular embodiment, the battery is used in a vehicle batteryapplication. In yet another particular embodiment, the battery is usedin a portable electronic device application.

In certain embodiments, the improved battery comprises: (1) an anode,(2) a cathode, and (3) an electrolyte capable of supporting reversibledeposition and stripping of metal at the anode, and reversibleintercalation and deintercalation of the metal at the cathode. Theimproved electrode composition may be used in one of the following typesof batteries: lithium-ion battery, aluminum-ion battery, magnesium-ionbattery, sodium-ion battery, metal-air (wherein the metal is lithium,aluminum, magnesium, zinc, or sodium) battery, and metal-sulfur (whereinthe metal is lithium, aluminum, magnesium, zinc, or sodium) battery. Inone particular embodiment, the improved electrode composition is used ina lithium-ion battery.

Anode

In certain embodiments, the anode comprises an active or basecomposition capable of intercalating metal ions during a charge cycleand deintercalating metal ions during a discharge cycle. In certainembodiments, the anode comprises lithium metal, including lithiumalloys. In some embodiments, the lithium is alloyed with aluminum. Insome embodiments, the anode comprises at least 80 wt. %, 90 wt. %, or 95wt. % lithium as the primary electrochemically active material.

In other embodiments, the anode composition comprises mesoporous metaloxide microspheres, such as those described in U.S. patent applicationSer. No. 13/372,795 and U.S. patent application entitled “MesoporousMetal Oxide Microsphere Electrode Compositions and Their Methods ofMaking,” being concurrently filed herewith, both applications of whichare incorporated by reference herein. In some embodiments, the metaloxide is a transition metal oxide selected from the group consisting oftitanium oxides (e.g., titanium dioxide and its polymorphs), vanadiumoxides, chromium oxides, manganese oxides, iron oxides, cobalt oxides,nickel oxides, copper oxides, zinc oxides, niobium oxides, tantalumoxides, molybdenum oxides, tungsten oxides, ruthenium oxides, palladiumoxides, cadmium oxides, zirconium oxides, hafnium oxides, andcombinations thereof. In one particular embodiment, the metal oxide is atitanium oxide.

In some embodiments, the average microsphere diameter is between 200 nmand 10 μm. In other embodiments, the average metal oxide microspherediameter is between 500 nm and 5 μm. In yet other embodiments, theaverage microsphere diameter is between 1 μm and 2 μm. In one particularembodiment, the average microsphere diameter is approximately 1 μm.

In certain embodiments, the mesopores in the microsphere structure havean average pore diameter between 1 nm and 50 nm. In other embodiments,the average pore diameter in the microsphere structure is between 5 nmand 20 nm. In yet other embodiments, the average pore diameter isbetween 10 nm and 15 nm. In one particular embodiment, the average porediameter in the microsphere structure is approximately 12 nm.

In certain embodiments, the microspheres in the mesoporous metal oxidemicrosphere structure are comprised of nanocrystallites or nanograinshaving an average grain diameter between 1 nm and 20 nm. In anotherembodiment, the average grain diameter of the nanocrystallites isbetween 5 nm and 10 nm. In one particular embodiment, the average graindiameter is approximately 6 nm.

In certain embodiments, the mesoporous metal oxide microsphere structurehas a surface area between 50 m²/g and 500 m²/g. In another embodiment,the surface area is between 100 m²/g and 300 m²/g. In anotherembodiment, the surface area of the mesoporous metal oxide microspherestructure is between 100 m²/g and 200 m²/g.

The conductivity of the anode may be improved by coating at least aportion of the base composition anode surface with a carbon-containingcomposition. The anode may be coated with a non-metal or metalloid dopedcarbon composition. In certain embodiments, the anode is coated with anitrogen-doped carbon composition. In one particular embodiment, theanode comprises lithium metal and a nitrogen-doped carbon coatingcomposition. The source of the nitrogen doping element in thenitrogen-doped carbon coating composition may be by annealing cathodesin flowing ammonia or nitrogen gas or by coating organic amines. Inparticular, the source of the nitrogen doping element in thenitrogen-doped carbon coating composition may include pyridine,1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide(EMIm-TFSI), 1-ethyl-3-methylimidazolium dicyanamide (EMIm-DCA), andmixtures thereof.

In certain embodiments, the coated anode comprises between 0.1-20 wt. %carbon, between 1-10 wt. % carbon, or between 4-8 wt. % carbon.Additionally, the coated cathode may comprise between 0.01-10 wt. %,0.05-5 wt. %, or 0.1-1 wt. % of the doping element (e.g., nitrogen).

Cathode

In certain embodiments, the cathode comprises a material capable ofintercalating the metal ions during a discharge cycle anddeintercalating the metal ions during a charge cycle. In certainembodiments, the cathode is a “high-rate” or “high current rate” cathodecapable of a fast charge and discharge capacity.

In certain embodiments, the cathode comprises an active materialselected from the group consisting of one or more phases: LiCoO₂,LiMn₂O₄, Li₂MnO₃, LiNiO₂, LiMn_(1.5)Ni_(0.5)O₄, LiFePO₄, Li₂FePO₄F,Li₃CoNiMnO₆, and Li(Li_(a)Ni_(x)Mn_(y)Co_(z))O₂. In one particularembodiment, the cathode comprises LiFePO₄.

In other embodiments, the cathode is selected from the group consistingof: λ-MnO₂ (or λ-Mn₂O₄) and V₂O₅. In some embodiments, the cathode is“LiM_(x)O_(y)” [herein defined as a cathode material comprising at leastone metal (M) and oxide (O)]. Non-limiting examples of LiM_(x)O_(y)cathodes include lithium cobalt oxide, lithium iron phosphate, andlithium manganese oxide.

In certain embodiments, the cathode isLi_(a)Mn_(1.5-b)Ni_(0.5-c)M_(d)O_(4-x), wherein M comprises any metalelement, including alkali metals, alkaline earth metals, transitionmetals, lanthanides, actinides, post-transition metals, or metalloids.In certain embodiments, “a” is between 0.5-2 or 1-1.4, “b” is between0-0.5, “c” is between 0-0.5 or 0-0.17, “d” is between 0-0.33, and “x” is0 or 1. In some embodiments, the value of “1.5-b”, “0.5-c,” and “d” addup to a value between 1 or 2. In some embodiments, the metal element isadded to the cathode material through a dopant compound. The dopantcompound may be a metal oxide. In certain embodiments, the metal (M) inthe cathode comprises an element selected from the group consisting of:Li, Na, K, Mg, Be, Ca, Sr, Ba, Si, Al, Ga, In, TI, Sc, Ti, V, Cr, Fe,Pt, Os, Cu, or Zn.

In certain embodiments, these active components can be mixed with acarbon material (such as carbon black, for example) to make themconducting, and mixed with a binder (such as PVDF binder inN-methylpyrrolidinole, for example) to hold the material together.

In other non-limiting examples, Ti(II) and Mn(II) complexes may also beconsidered as a transition element for the cathode material.

In another embodiment, the cathode material is λ-MnO₂. In certainembodiments, the cathode material can be prepared in a “reduced” oruncharged state by reacting MnO₂ with butyllithium for Li-ion batteries.The cathode may then be “charged” by oxidation of the Mn oxide resultingin expulsion of Li⁺ ions.

Spinel-type MnO₂ may be made by treating LiMn₂O₄ with aqueous acid. Thisλ-MnO₂ has the same structural framework of spinel, but with most of thelithium removed from the tetrahedral sites of the spinel lattice. Themechanism for the conversion of LiMn₂O₄ to λ-MnO₂ involves adisproportionation of the Mn³⁺ ions into Mn⁴⁺ (remains in the solid) andMn²⁺ (leaches out into the aqueous solution).

In some embodiments, the conductivity of the cathode composition may beimproved by coating the surface of the cathode with a carbon-containingcomposition. The cathode may be coated with a non-metal or metalloiddoped carbon composition. In some embodiments, the cathode is coatedwith a nitrogen-doped carbon composition. In one particular embodiment,the cathode comprises LiFePO₄ and a nitrogen-doped carbon coatingcomposition. Non-limiting examples for the source of the nitrogen dopingelement in the nitrogen-doped carbon coating composition includepyridine, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIm-TFSI), 1-ethyl-3-methylimidazolium dicyanamide (EMIm-DCA),and mixtures thereof. In certain embodiments, the coated cathodecomprises between 0.1-20 wt. carbon, between 1-10 wt. % carbon, orbetween 4-8 wt. % carbon. Additionally, the coated cathode may comprisebetween 0.01-10 wt. %, 0.05-5 wt. %, or 0.1-1 wt. % of the dopingelement (e.g., nitrogen).

In other embodiments, the cathode properties (e.g., conductivity,capacity retention) may be improved by chemically modifying the surfaceof the cathode through an annealing reaction. The annealing reaction maybe conducted in a reducing atmosphere to at least partially reduce themetal in the cathode. For example, the reducing atmosphere may include avacuum or flowing reducing gas to at least partially reduce the metal inthe composition. In certain embodiments, the reducing atmosphere is aninert gas. In some embodiments, the reducing atmosphere is a vacuum. Inother embodiments, the reducing atmosphere contains a gas selected fromthe group consisting of: hydrogen, argon, nitrogen, fluorine, sulfur,carbon monoxide, methane, ammonia, carbon dioxide, and mixtures thereof.In one particular embodiment, the annealing reaction is conducted inflowing ammonia gas (i.e., the cathode composition is subjected to anitridation reaction). In some embodiments, the annealing reaction iscarried out at a temperature between 300-800° C., 500-700° C., or 550°C. for a time between 30 minutes and 24 hours, or between 1-15 hours,with a reducing gas (e.g., ammonia) flow rate of approximately 1mL/min-500 mL/min or about 200 mL/min for 0.5-2 g of cathode material.

In one particular embodiment, the cathode is a LiMn_(1.5)Ni_(0.5)O₄ or adoped metal cathode (Li_(a)Mn_(1.5-b)Ni_(0.5-c)M_(d)O₄) (spinel), and isannealed in a flowing ammonia gas atmosphere. Such uniformly dispersedoxy-nitride, metal nitride, or dissolved/adsorbed nitrogen on activeLi_(a)Mn_(1.5-b)Ni_(0.5-c)M_(d)O₄ (spinel) cathode material can providea high capacity retention, continuous chemical stability, tolerance ofmanganese dissolution at high temperature, improved electronconductivity, and/or reduced irreversible capacity loss. Controlledsurface of the active material may have a low resistance and enhance thesurface intercalation reaction of a lithium ion, reduce cellpolarization, and/or inter-particle resistance and contact betweenactive electrode material and electrolyte. Furthermore, an annealedspinel material may offer a viable, low-cost approach with a powerdensity value much higher than that of the other cathode materials, suchas LiCoO₂, LiMn₂O₄, and LiFePO₄. In certain embodiments, the annealedspinel cathodes may have a capacity exceeding 120 mAh/g or 130 mAh/g atvarious discharge rates, such as C/10, 1 C, 3 C, 5 C, and 10 C.

Electrolyte

Suitable electrolytes for the battery are electrochemically stablecompositions within the operation window of the electrodes. In otherwords, in certain embodiments, a suitable electrolyte is one that iscapable of supporting reversible deposition and stripping of metal atthe anode, and reversible intercalation and deintercalation of metal atthe cathode. Suitable electrolytes may include materials that assist inachieving a wide electrochemical window, good ionic conductivity,improved rate capability, long cycle ability, good capacity retention,and compatibility with the anode and cathode materials.

In certain embodiments, the electrolyte is a metal salt. The metal saltmay be dissolved in an organic solvent such as ethylene carbonate,dimethyl carbonate, diethyl carbonate, and combinations thereof. In someembodiments, the battery is a lithium-ion battery and the electrolyte isa lithium salt selected from the group consisting of: LiPF₆, LiBF₄, andLiClO₄.

In certain embodiments, the electrolyte materials may be optimizedthrough the addition of suitable co-solvents that may assist in reducingviscosity (increasing mobility) and/or increasing charge transfer number(increasing salt dissociation).

Performance

In certain embodiments, an electrode or battery comprising an electrodecoated with a doped carbon composition has an improved capacity over anuncoated electrode or undoped carbon coated electrode. Further, incertain embodiments, an electrode or battery comprising an electrodecoated with a nitrogen-doped carbon composition has an improved capacityin comparison to a similar undoped carbon coated electrode. In someembodiments, the doped carbon coated electrode has at least a 10%improved capacity at 3 C, or at least a 30% improved capacity at 5 C.

In certain embodiments, the doped carbon coated electrodes (e.g.,nitrogen-doped carbon coated LiFePO₄) have a capacity (rate performance)of at least 125 mAh/g at a rate of C/10, a capacity of at least 100mAh/g at a rate of 3 C, or a capacity of at least 80 mAh/g at a rate of5 C. In one particular embodiment, a nitrogen doped carbon coatedLiFePO₄ cathode has a capacity of approximately 125 mAh/g at C/10, 120mAh/g at 1 C, 110 mAh/g at 3 C, or 98 mAh/g at 5 C.

In certain embodiments, a cathode that has undergone an annealingreaction has an improved capacity over an unreacted cathode. In someembodiments, the annealed cathode has a capacity of at least 120 mAh/gor 130 mAh/g at C/10, 1 C, 3 C, 5 C, or 10 C. In some embodiments, theannealed cathode has at least a 125% or 150% improved capacity over asimilar, untreated cathode at 3 C, 5 C, or 10 C. In one particularembodiment, an annealed LiMn_(1.5)Ni_(0.5)O₄ spinel cathode has at leasta 125% or 150% improved capacity over a similar, untreatedLiMn_(1.5)Ni_(0.5)O₄ spinel cathode at 3 C, 5° C., or 10 C.

In certain embodiments, the battery comprising a doped carbon coatedelectrode (e.g., nitrogen-doped carbon coated LiFePO₄) has an improvedcharge and discharge rates. In some embodiments, the battery candischarge 50% of the full range capacity in approximately 6 minutes. Inother embodiments, the battery can be charged from 0% to 50% of the fullrange capacity in 6 minutes. In yet other embodiments, the battery canbe discharge 33% of the full range capacity in approximately 1 minute.In certain embodiments, the battery can be charged from 0% to 33% of thefull range capacity in 1 minute.

In certain embodiments, the battery is a secondary battery capable ofhaving at least 100, 1000, 5000, or 10000 cycles prior to batteryfailure. In some embodiments, battery failure is related to thefunctional discharge capacity becoming only 50%, 60%, 70%, 80%, or 90%of the initial discharge capacity after a number of cycles. In otherembodiments, battery failure is related to the inability to recharge thebattery due to dendrite formation, oxide film formation, or otherbuildup on the anode or cathode. In one particular embodiment, thebattery is capable of having a functional discharge capacity greaterthan 50% of the initial discharge capacity after 100 cycles. In anotherembodiment, the secondary battery is capable of having a functionaldischarge capacity greater than 90% of the initial discharge capacityafter 100 cycles.

Methods of Making

In certain embodiments, methods of making the battery comprise providingan anode. In certain embodiments, the methods further comprise providinga high-rate capable cathode. In certain embodiments, the methods furthercomprise providing an electrolyte capable of supporting reversibledeposition and stripping of metal at the anode, and reversibleintercalation and deintercalation of the metal at the cathode. The anodemay comprise lithium metal or a lithium alloy. In some embodiments, theanode comprises at least 80 wt. %, 90 wt. %, or 95 wt. % lithium as theprimary electrochemically active material. In other embodiments, theanode comprises a mesoporous metal oxide microsphere composition, suchas those described in U.S. patent application Ser. No. 13/372,795 andU.S. patent application entitled “Mesoporous Metal Oxide MicrosphereElectrode Compositions and Their Methods of Making,” being concurrentlyfiled herewith, both applications of which are incorporated by referenceherein.

In some embodiments, the surface of the anode may be coated with a dopedcarbon composition, such as a non-metal or metalloid doped carboncomposition. In some embodiments, the anode is coated with anitrogen-doped carbon composition. In one particular embodiment, theanode comprises lithium and a nitrogen-doped carbon coating composition.

In certain embodiments, the surface of the cathode (e.g., LiFePO₄) maybe coated with a doped carbon composition, such as a non-metal ormetalloid doped carbon composition. In some embodiments, the cathode iscoated with a nitrogen-doped carbon composition. In one particularembodiment, the cathode comprises LiFePO₄ and a nitrogen-doped carboncoating composition. Non-limiting examples for the source of thenitrogen doping element in the nitrogen-doped carbon coating compositioninclude pyridine, 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl) imide (EMIm-TFSI),1-ethyl-3-methylimidazolium dicyanamide (EMIm-DCA), and mixturesthereof. The coating step may be conducted through a hydrothermalprocess followed by post-annealing in the presence of an ionic liquid.For example, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIm-TFSI) can be mixed with an cathode (e.g., LiFePO₄) powderand heated at an elevated temperature in a flowing inert gas atmosphere.In certain embodiments, the mixture may be heated to at least 300° C.,at least 500° C., or at least 700° C. The inert gas atmosphere may be anoble gas, such as argon. The time held at the elevated temperature maybe at least 30 minutes, at least 60 minutes, or at least 90 minutes. Inone particular embodiment, the coating step involves mixing1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide(EMIm-TFSI) with LiFePO₄ powder and heating the mixture to 700° C. in aflowing argon atmosphere for 90 min.

In certain embodiments, the coating over the surface of the cathode isbetween 1-100 nm, 5-50 nm, or 10-15 nm in thickness. The coated cathodecomposition may comprise between 0.1-20 wt. % carbon, between 1-10 wt. %carbon, or between 4-8 wt. % carbon. Additionally, the coated cathodecomposition may comprise between 0.01-10 wt. %, 0.05-5 wt. %, or 0.1-1wt. % of the doping element (e.g., nitrogen, chromium).

In some embodiments, batteries for grid storage applications may beformed using the improved electrode compositions described. In otherembodiments, batteries for vehicle applications may be formed. In yetother embodiments, batteries for military applications may be formed. Inyet other embodiments, batteries for portable electronic devices may beformed. In some embodiments, batteries for medical device applicationsmay be formed. In certain embodiments, batteries for standard cell sizebattery applications may be formed.

While the invention as described may have modifications and alternativeforms, various embodiments thereof have been described in detail. Itshould be understood, however, that the description herein of thesevarious embodiments is not intended to limit the invention, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the claims. Further, while the invention will also bedescribed with reference to the following non-limiting examples, it willbe understood, of course, that the invention is not limited theretosince modifications may be made by those skilled in the art,particularly in light of the foregoing teachings.

EXAMPLES

Various chemically modified cathodes were formed and tested for theirperformance characteristics.

Example 1 Nitrogen Doped Carbon Coated LiFePO₄ Electrode

Rod-like LiFePO₄ with a nitrogen-doped carbon layer was prepared by thefollowing procedure. First, the rod-like LiFePO₄ powders were obtainedby hydrothermal reaction. An aqueous solution of LiOH and glucose wasfirst stirred for 1 h. An aqueous solution of the iron sulfateheptahydrate (FeSO₄.7H₂O, 99%, Alfa) and ammonium hydrogen phosphate((NH₄)₂HPO₄, 99%, Alfa) was then added to this mixture so that theLi:Fe:P molar ratio was 2:1:1 and Fe²⁺ to glucose molar ratio was 2:1.40 mL of the transparent solution obtained was transferred into a 100 mLTeflon-lined autoclave and heated at 220° C. for 24 h with aheating/cooling rate of 2° C./min. The resultant slurry was thenfiltered and washed with deionized water (DI water) before drying in avacuum oven. Different amounts of 0.1 mL, 0.2 mL, and 0.3 mL1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide(EMIm-TFSI) were mixed with 0.5 g of as-prepared rod-like LiFePO₄powders (the obtained samples were named as Sample 1, Sample 2, andSample 3), respectively. Samples 1, 2, and 3 were heated to 700° C. inflowing argon atmosphere for 90 min.

Example 2 Annealing/Nitridation of Li_(a)Mn_(1.5-b)Ni_(0.5-c)M_(d)O₄Cathode

An annealed cathode is prepared by providing a cathode materialcomprising Li_(a)Mn_(1.5-b)Ni_(0.5-c)M_(d)O₄, The cathode material isthen annealed under NH₃ gas at 550° C. (ammonolysis), with a NH₃ flowrate of 200 mL/min, for between 1 and 15 h. The annealing processresults in forming a conducting nitradated cathode material.

Material Characterization:

The compositions can be characterized with a Scintag X-raydiffractometer with Cu Kα radiation, Perkin-Elmer series 7 ThermalAnalysis System thermo-gravimetric analysis (TGA), Thermo X-rayphotoelectron spectrometer (XPS), WITec Raman spectroscopy with a 512 nmlaser excitation, Hitachi S-4800 FEG scanning electron microscope (SEM),Hitachi HF-3300 transmission electron microscope (TEM), andelectrochemical charge-discharge measurements.

Electrochemical Evaluation:

Regarding the doped coated cathodes, the electrodes were fabricated witha slurry consisting of 70 wt. % of the as-synthesized active materialLiFePO₄ composition, 20 wt. % carbon black (e.g. Super-S or Super 45carbon black), and 10 wt. % polyvinylidene fluoride (PVDF) dissolved inN-methyl-2-pyrrolidone (NMP). The electrodes were spread onto analuminum foil and were dried in a vacuum oven at 120° C. forapproximately 12 hours before transferring into an Argon-filled glovebox.

Regarding the annealed cathodes (via nitridation), the electrodes werefabricated with a slurry consisting of 80 wt. % of the as-synthesizedannealed cathode material was spread onto an aluminum foil, 10 wt. %carbon black (Super 45 carbon black), and 10 wt. % polyvinylidenefluoride (PVDF) dissolved in N-methyl-2-pyrrolidone (NMP). Theelectrodes were dried in a vacuum oven before transferring into anArgon-filled glove box.

Coin cells (CR2032) were fabricated using lithium metal as the counterelectrode, Celgard 2325 as the separator, and LiPF₆ (1 M) in ethylenecarbonate/dimethyl carbonate/diethyl carbonate (EC/DMC/DEC, 1:1:1 vol.%) or ethylene carbonate/diethyl carbonate (1:1 vol. %) as theelectrolyte.

The cells could be tested using an Arbin BT2000 charger and a PrincetonApplied Research VersaSTAT 4 potentiostat. Certain charge-dischargeexperiments were performed galvano-statically at a constant currentdensity of 15.2 mA/g (C/10) of active material within the voltage rangeof 2 and 4.3 V vs. Li/Li⁺ or between 3.5 and 5.0 V. Certainelectrochemical impedance spectroscopic analyses (EIS) were carried outwith a VersaSTAT 4 by applying a 10 mV amplitude signal in the frequencyrange of 10 kHz to 0.01 Hz.

Results:

The XRD patterns of rod-like LiFePO₄ coated with nitrogen-doped carbonlayers are shown in FIG. 1(a). For all of the samples obtained, all ofthe reflections could be indexed on the basis of the orthorhombicLiFePO₄ olivine structure-type (Pnma, JCPDS No. 81-1173).

The carbon content in the coated LiFePO₄ specimens was calculated usingTGA methods, as shown in FIG. 1(b). They show a weight losscorresponding primarily to the removal of carbon from the samples asCO₂, indicating that samples 1, 2 and 3 evolve to approximately 12, 14,and 18 wt. % nitrogen-doped carbon, respectively. Sample 1 was furtherinvestigated by Raman spectroscopic analysis, as shown in FIG. 1(c). Themodes at 1582 and 1357 cm⁻¹ correspond to, respectively, the G (ordered)and D (disordered) bands. The integrated intensity ratio ID/IG is anindication of the degree of graphitization. A high intensity ratio of0.9, as compared to 0.09 in ordered synthetic graphite indicates ahigher degree of disorder for the carbon present in the coated LiFePO₄.

The XPS survey spectra of coated LiFePO₄ rods are shown in FIG. 1(d).The peaks of P 1s, C 1s, N 1s, O 1s, and Fe 2p can be seen. MultipleC-bonding configurations were observed that were consistent with C/O andC/N bonding. Likewise, the N 1s spectra showed multiple bondingconfigurations, also consistent with C/N bonding.

FIGS. 2(a) and 2(b) show electrochemical performances for coatedrod-like LiFePO₄ samples. The cyclability of the coated rod-like LiFePO₄for all three samples between 4.3 and 2 Vat C/10 are compared in FIG.2(a). All three coated LiFePO₄ samples show good cyclability.Particularly, Sample 1 exhibits the best capacity retention of 122 mAh/gafter 30 cycles among the three rod samples. The improved cyclability isrelated to the nitrogen-doped carbon layer and favorable morphology ofthe material, which is consistent with reports that coatings provideenhanced electrical conductivity between the substrate and theelectrode. The rate and cycling performance of the coated rod-likeLiFePO₄ samples are shown in FIG. 2(b). For comparison, a rod-likeLiFePO₄ sample coated with carbon but without nitrogen (LiFePO₄—C) wasprepared using glucose. The coated LiFePO₄ samples exhibit significantlyhigher rate capability than the LiFePO₄—C sample; for example, thecoated sample retains a high capacity of 98 mAh/g at 5 C rates comparedto a capacity of 73 mAh/g for the LiFePO₄—C sample, which implies thatcoated samples have a lower polarization inside the electrode.

FIG. 3 compares the discharge capacity/rate capability between anuntreated LiMn_(1.5)Ni_(0.5)O₄ cathode, and various LiMn_(1.5)Ni_(0.5)O₄cathodes that have undergone annealing/nitridation reactions for variousperiods of time (i.e., 30 min, 1 hour, 5 hours, and 10 hours). Themodified/annealed samples exhibit improved rate capabilities over theuntreated sample, and show stability even at 10 C.

What is claimed is:
 1. An electrode for a battery comprising: a cathode;the cathode having a base composition having an active material capableof intercalating metal ions during a discharge cycle and deintercalatingthe metal ions during a charge cycle, wherein the active material isLiFePO₄; and the cathode further having approximately 10-12% by weightof a nitrogen-doped carbon coating composition, the nitrogen-dopedcarbon coating composition covering at least a portion of the basecomposition and having a thickness of 5-50 nm, wherein the basecomposition does not contain nitrogen; wherein the nitrogen-doped carboncoating composition comprises a nitrogen doping element derived from1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.
 2. Theelectrode of claim 1, wherein the capacity is at least 10% greater at 3C, or at least 30% greater at 5 C, when compared with a cathode havingthe same base composition without a coating composition.
 3. Theelectrode of claim 1 wherein the nitrogen-doped carbon coatingcomposition has a thickness of 10-15 nm.
 4. The electrode of claim 1,wherein the nitrogen-doped carbon coating composition is a non-oxidecontaining composition.
 5. An electrode for a battery comprising: acathode; the cathode having a base composition having an active materialcapable of intercalating metal ions during a discharge cycle anddeintercalating the metal ions during a charge cycle, wherein the activematerial is LiFePO₄; and the cathode further having approximately 10-12%by weight of a nitrogen-doped carbon coating composition, thenitrogen-doped carbon coating composition covering at least a portion ofthe base composition and having a thickness of 5-50 nm, thenitrogen-doped carbon coating composition is a non-oxide containingcomposition, and wherein the base composition does not contain nitrogen;wherein the nitrogen-doped carbon coating composition comprises a bulkdisordered graphite material; and wherein the cathode has a capacity ofat least 110 mAh/g at a rate of 3 C, or at least 98 mAh/g at a rate of 5C, wherein the nitrogen-doped carbon coating composition comprises anitrogen doping element derived from 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide.
 6. A battery comprising: an anodehaving a base composition; a cathode having a base composition with anactive material capable of intercalating metal ions during a dischargecycle and deintercalating the metal ions during a charge cycle, whereinthe active material is LiFePO₄; the cathode further having approximately12% by weight of a nitrogen-doped carbon coating composition that coversat least a portion of the base composition of the cathode and that has athickness of 5-50 nm, the nitrogen-doped carbon coating composition is anon-oxide containing composition, and wherein the base composition doesnot contain nitrogen; and an electrolyte capable of supportingreversible deposition and stripping of metal at the anode, andreversible intercalation and deintercalation of the metal at thecathode; wherein the cathode has a capacity of at least 125 mAh/g at arate of C/10, at least 120 mAh/g at a rate of 1 C, at least 110 mAh/g ata rate of 3 C, or at least 98 mAh/g at a rate of 5 C, wherein thenitrogen-doped carbon coating composition comprises a nitrogen dopingelement derived from 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide.
 7. The battery of claim 6, whereinthe capacity is at least 10% greater at 3 C, or at least 30% greater at5 C, when compared with a cathode having the same base composition andan undoped carbon coating composition.
 8. The battery of claim 6,wherein the base composition of the anode comprises at least 90 wt. %lithium as the primary electrochemically active material of the anode.9. The battery of claim 6, wherein the base composition of the anodecomprises mesoporous metal oxide microspheres, having (a) microsphereswith an average diameter between 200 nm and 10 μm, and (b) mesopores onthe surface and interior of the microspheres, wherein the mesopores havean average diameter between 1 nm and 50 nm and the microspheres have asurface area between 50 m²/g and 500 m²/g.
 10. The battery of claim 6,wherein the battery is selected from the group consisting of thefollowing battery types: lithium-ion, aluminum-ion, magnesium-ion,sodium-ion, metal-air, and metal-sulfur, wherein the metal is lithium,aluminum, magnesium, zinc, or sodium.
 11. The battery of claim 6,wherein the battery is a lithium-ion battery.
 12. The battery of claim 6having an ability to charge from 0% to 50% of the full range capacity in6 minutes, or an ability to charge from 0% to 33% of the full rangecapacity in 1 minute.
 13. The battery of claim 6 having a functionaldischarge capacity of at least 90% of the initial discharge capacityafter 100 cycles.
 14. The battery of claim 6, wherein the battery isused in a grid storage application, vehicle battery application,military application, portable electronic device application, medicaldevice application, or standard cell size battery application.
 15. Thebattery of claim 6 wherein the nitrogen-doped carbon coating compositionhas a thickness of 10-15 nm.
 16. A method of forming a coated electrodecomprising: providing a cathode having a base electrode compositionhaving an active material of LiFePO₄; providing a nitrogen-doped carboncoating composition; and mixing the coating composition with the baseelectrode composition at an elevated temperature in a flowing inert gasatmosphere, wherein the nitrogen-doped carbon coating composition is anitrogen-doped carbon composition having a nitrogen doping element from1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide,wherein the cathode further having approximately 10-12% by weight of thenitrogen-doped carbon coating composition, the nitrogen-doped carboncoating composition covering at least a portion of the base electrodecomposition and having a thickness of 5-50 nm, wherein the baseelectrode composition does not contain nitrogen; wherein the cathode hasa capacity of at least 110 mAh/g at a rate of 3C, or at least 98 mAh/gat a rate of 5 C.